The present invention relates to an adjustable metering valve for an internal combustion engine fuel injector.
A metering valve is normally controlled by the armature of an electromagnet, and is fitted to the injector body; and, as the travel or lift of the armature towards the core of the electromagnet affects supply by the injector, while the gap between the armature and the core affects the response of the valve when the electromagnet is deenergized, both travel and gap must be adjusted accurately.
Various metering valves are known in which the armature is connected to a stem guided by a sleeve having a stop flange; and the travel of the armature is defined by the flange arresting against an edge of the sleeve. In one known metering valve, the sleeve is fitted inside the injector via the interposition of a shim, and the electromagnet is fitted to the injector body by means of a skirt and via the interposition of a second shim. In another known metering valve, the flange of the guide sleeve is fitted between a shoulder of the sleeve and an edge of the electromagnet skirt via the interposition of two sets of shims.
In both cases, the two shims are selected from a number of calibrated shims of modular thicknesses differing by a very small amount, which, as is known, for technical reasons, may not be less than the machining tolerances involved, e.g. five microns. A five-micron tolerance, however, represents a fairly rough adjustment in the travel of the armature, so that it is often impossible to keep supply by the injector within the strict limits required by modern, in particular high-power, internal combustion engines.
One injector has been proposed in which the sleeve comprises a threaded member directly engaging an internal thread on the injector body to adjust the travel of the armature by adjusting the tightening torque of the threaded member. Such an injector, however, involves disassembling part of the injector itself.